Electronic switching means



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@da KOPF-.DIZOU mmJDm Jur-211C ...ShzwDGwm INVENTOR. ROBERT B.TROUSDALE ATTORN EY United States Patent O ELECTRoNIc swircrnNG MEANS Robert B. Trousdale, Webster, N. Y., assignor, by mesne assignments, to General Dynamics Corporation, a corporation of Delaware Original application April 23, 1954, Serial No. 425,022. Divided and this application March 11, 1955, Serial No. 494,509

3 claims. (ci. 25o- 21) This invention relates to telephone systems and more particularly to electronic switching means for use in automatic telephone systems. A system of this type is shown and described in my co-pending application, Serial No. 425,092, tiled April 23, 1954, of which this invention is a division.

lt is an object of this invention to provide a new and improved telephone system in which some or substantially all mechanical relays or step-by-step switches are eliminated at a reasonable cost and which is eflicient and positive in operation, inexpensive to maintain, and relatively simple to install and maintain.

lt is another object of my invention to provide a new and improved nding means of an electronic type operating on pulse multiplex principles and having provision for allotting each finder to a calling line, for rendering each seized finder circuit inoperative to calls on any except that particular calling line, and for preventing loss of a seized finder during dialing or because of the accidental or temporary loss of signal pulses, as for example, hook switch tumbling, slow dialing, etc.

It is a more particular object of this invention to provide a new and improved timing circuit for rendering each seized linder circuit inoperative to calls on any lines other than the calling line with which it is associated.

The automatic telephone system described and claimed herein utilizes a finder the operation of which is based upon a principle which may be termed, for convenience, the time elapse principle and utilizes pulse transmission, the pulses representing the various calling lines being multiplexed or intermixed.

In carrying out the principles of this invention, pulse transmission is based upon the utilization of pulses to take spaced samples of the desired signal or intelligence to be conveyed. The effect is the same as plotting a smooth continuous curve from a few points by assuming that a uniform change takes place between them. lf more detail is required, more samples or points are taken.

A simple sine wave may be reconstructed, both as to frequency and amplitude, by employing only two samples per cycle. From the Fourier theorem that any complex wave can be synthesized by properly combining sine waves, it is evident that speech can be transmitted at a sampling rate suitable for the highest desired harmonic. Practical filter limitations make it desirable to sample at a rate approximately two and one-half times the highest desired frequency. lt should be noted that the width of the sample is of very little importance to the reconstruction providing it is no more than one half as wide as a cycle of the highest desired frequency. The pulse carrier bandwidth is determined by the width of the pulse itself, however, for the narrower the pulse, the wider the band. Modulation has no effect upon the bandwidth. A single pulse sample contains information only as to the voltage of the sampled signal at that instant. This information can be impressed in a number of ways such as pulse height, width, or displacement.

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Several audio signals may be transmitted over a single channel by merely staggering the positions of pulse samples. The several signals may be separated at the receiving terminal. Bandwidth utilization is comparable to that of conventional frequency displacement (carrier) systems but the overall economy is greater due to the realtively simple equipment needed to combine and separate the several signals- Multiplex equipment is also compact and either of these factors is far more important in a telephone exchange than in toll transmission networks where pulse methods are already applied.

ln accordance with the preferred embodiment of this invention, there is provided a gate which may resemble closely an amplifier, employing one or more electron discharge devices, and which may be called for convenience, an in-gate. An allotter is provided for successively enabling or preparing for conduction upon receipt of a signal pulse the various nder in-gates for a predetermined period, as one frame of signal pulses, a frame cornprising a time period permitting a pulse corresponding to each line in the group to be multiplexed. The circuits are arranged so that only one in-gate is enabled by the operation oi the allotter at any one time whereby each finder is successively available for the duration of one frame.

Each signal pulse corresponding to a seizing line is passed through the tinder to succeeding circuits. In addition cach passing signal pulse is utilized to close the ingatc immediately after the passage of the pulse to prevent the allotted finder from being affected by the allotter during the remainder of the call, to transmit outgoing lockout pulses to all other linders at the time positions corresponding to the calling line throughout the duration of the call, and to start a frame timer for re-enabling the in-gate amplier at the expected times of the succeeding pulses corresponding to the calling line.

lt should be remembered that the elapsed time between each signal pulse corresponding to a given subscribers line, regardless of its time position within the frame, is the same and equal to the duration of a frame. The frame timing means is, therefore, arranged to measure oil an identical period starting immediately after each desired signal pulse is received and ending just before the next signal pulse representing the same line appears at the in-gate. The frame timer re-opens the gate just in time to pass the next correct signal pulse whereupon the whole process is repeated successively until no more signal pulses are received.

The nder is thereby controlled to accept only signal pulses having the same time positions as the signal pulse which caused the finder to seize the calling line and other finders are rendered incapable of accepting pulses corresponding to the time position of a calling line because of the lockout pulses which paralyze their in-gates at that time position.

t is desired to prevent loss of a finder because of temporary or accidental loss of signal pulses, due to dialing, etc. F or this purpose, there is contemplated provision of an auxiliary gate for the purpose of introducing a train of dummy or auxiilary pulses occurring at the same rate as the signal or multiplexer pulses and which have identical time positions as the signal pulses. These auxiliary pulses are utilized to assist in the switching and timing functions referred to above. To prevent loss of a nder by accidental or temporary loss of pulses for any reason, delay means is associated with the auxiliary gate amplifier as, for example, by providing a resistance-capacity network charged by signal pulses, the time constant being sufliciently long so that momentary interruptions do not stop the ow of auxiliary or control pulses into the finder. This feature of the herein described and illustrated system is not my invention but is the invention of Frank A.

Morris, assigned to the same assignee as my invention and described, illustrated, and claimed in copending application Serial No. 425,093, led April 23, 1954.

The system to be described is based upon decimal principles. Lines are preferably grouped by tens, and each group of ten lines is provided with a multiplexing circuit, the multiplexing circuit being arranged to sample each line and to combine pulses representing the samples into a single train of pulses- There is provided, for overall control purposes, a suitable source of pulses of a suitable frequency, as for example, 100 kilocycles. The pulses obtained from this source are commutated and employed for sampling each line successively in the multiplexer. The output of the multiplexer, therefore, comprises a succession of frames of pulses, each frame including ten equally spaced pulses corresponding successively to the ten lines of the calling group. Thus, each frame is divided into ten periods, corresponding periods in each frame representing the same line. The pulses may be modulated by an audio or signal voltage representing the sounds "f or other intelligence to be communicated or by dial impulses.

The activation of a line by a subscriber, as by lifting his receiver, causes pulses to appear at the finders at regular intervals, the exact time positions of the pulses being dependent upon the particular line activated. Speech and dialing signals are conveyed by these pulses by a form of amplitude modulation, the multiplexed pulses being provided at a relatively high repetition rate as, for example, ten kilocycles per second.

Common equipment may be shared by incorporating a plurality of line finders, as four, for example, to constitute a group, within which each finder is connected to all subscribers lines included in the particular nlultiplexed group associated with this group of finders.

The primary purpose of each line nder is to pass multiplexed pulses to succeeding equipment. Secondary purposes include the generation of lockout pulses to be transmitted or impressed upon other finders in the group to cause such other finders to ignore the signals representing the calling line which has been seized, as for example, by sending suitable pulses to the other finders to cut ofi or close their in-gates, i. e., prevent allotter pulses from opening the gates included in the other nders for the duration of the lockout pulses. If the lockout pulses are timed to straddle the time locations of the found or seized line pulses, the lockout pulses do not affect adjacent multiplexed pulses corresponding to other lines in the calling group.

Other objects and advantages of my invention will bet come apparent as the following description proceeds, and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of my invention, reference may be had to *i the accompanying drawings in which:

Figs. 1 and 2 show in block diagram form different embodiments of my invention;

Fig. 3 illustrates a suitable pulse generator for use in my system;

Fig. 4 illustrates a typical line circuit and a suitable multiplexer circuit embodying the principles of my invention;

Fig. 5 illustrates the basic features of a suitable sequential generator for use in the telephone system disclosed herein;

Fig 6 shows typical circuits for a channel pulse commutator for use with the foregoing components of a system;

Figs. 7, 8 and 9 when taken together illustrate a finder embodying the principles of my invention;

Fig. 10 discloses a suitable connector for use in the system described herein;

Fig. 10A discloses a suitable outgate for use in my system;

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Figs. 11, 12 and 13 illustrate typical conditions in the system descirbed herein;

Fig. 14 is a chart illustrating the proper relationship of Figs. 3 to 10A, inclusive, these figures when laid next to each other as indicated, illustrating a one way communication system;

Fig. 15 shows in block form an arrangement utilizing the principles of my invention for providing two-way communication;

Fig. 16 shows a modification of Pig. 15;

Figs. l7, 18 and 19 show alternate forms of multiplexers;

Fig. 20 illustrates a timing circuit which may be ernployed in my system.

In Fig. 1 there are illustrated components of a system, shown in block form, for accomplishing the previously described functions. There is provided a suitable sequential pulse generator for sequentially causing a multiplexing device 141 to sample successively the line circuits 142 assigned to that particular multiplexer. In the output of the multiplexer there appears a train of pulses, each pulse representing a calling line and having a time position within each frame or complete cycle represeting a single sampling of each line in the calling group of lines including the calling line. The relationship of input and output pulses with respect to multiplexer 141 are shown in Fig. 12A and Fig. 12B, respectively- The output from multiplexer 141 comprises, in a single frame, one or more successive pulses depending upon the number of lines in ofi-hook or calling condition.

For each group of lines there is provided a plurality of finders. I have shown four finders, finder No. l being indicated by the numeral 144.

Each finder is allotted successively for a single frame to test for calling lines, i. e., is made responsive to multiplexer output pulses, by means of suitable signal or coutrol quantities, such as suitable pulses from a suitable allotter 143. Assuming that the allotter has allotted finder 144, in-gate 144a is made responsive to pulses received from multiplexer 141. Pulses passing through ingate 144:1 are forwarded through succeeding equipment such as connector 145, and distributor 146 to the called line, as 147, for example.

Each finder of the type shown in Fig. l is provided with a trigger circuit 148 and a timing circuit 149. Each signal pulse passing through in-gate 144:1 is utilized to block or cut-off in-gate 144e immediately after passage 0f the pulse and to trigger circuit 148 to start a timing cycle arranged to re-Open or again enable iti-gate 1440: at such a time as to pass the next pulse corresponding to the seized calling line. Each pulse is also utilized to block and maintain blocked the allotter gate 150 so that finder No. l cannot be allotted to another call. Pulses are also conducted to the other nders in the tinder group to prevent operation of the other lindcrs in response to pulses representing the line seized by nder No. l.

Thus, there is provided a finder arranged to accept and pass only signal pulses having the same time position as the pulse which triggered it.

Means is provided for connecting an extended calling line to a called line including a connector 145 and distributor 146. Connector 145 may comprise means to translate the signal pulses into a step representation of the signal being communicated. The translator is generally represented by numeral 151. In order to choose the called line, dial impulse counting means 152 is utilized to trigger a suitable network 153 at a time corresponding to the time position of the called line to open out-gate 154 to resample the audio voltage or signals. Network 153 may be prepared for operation or enabled by means of a reference pulse generator 155 operating in synchronism with pulse generator 140. If desired, generators 140 and 155 may be a single source of pulses. Connector 145 accepts pulses having a time position corresponding to the calling line and forwards or re-transmits pulses in a new time position corresponding to the desired line. The new time position is determined by the network 153 which, in elect, measures off the time between a reference and the time position of the called line which control is determined by dialing at the calling station. The new pulse is released just as the distributor is in condition to pass pulses to the called line. The distributor may comprise a circuit similar to that used in the multiplexer 141.

There is illustrated in Fig. 2 a modification, shown and claimed in the above-identified copending application, utilizing auxiliary or dummy control pulses to avoid loss of connections by slow or faulty dialing, flashing. etc. With this arrangement, instead of employing signal pulses to trigger the timing circuit, the signal pulses are utilized to enable or prepare an auxiliary gate 156 for operation upon receipt of auxiliary or control pulses in synchronism with the multiplexed pulses. Separate pulse sources may be used but a single pulse generator 140 as indicated in Fig. 2 is preferable. The auxiliary gate is held open by a suitable slow release or holding circuit 157 such as a resistance-capacity network charged by signal pulses so that momentary or accidental interruptions do not release the finder.

In order to simplify an understanding of this invention. the disclosure has been limited to the essential features of the invention and functions which are not intimately connected with the subject matter claimed herein, such as dial tone, ringing, and busy tone, for example, have been omitted, such features being shown and described in detail in a copending application of Frank A. Morris and Robert B. Trousdale, Serial No. 134,974, led December 24, 1949, and assigned to the same assignee as the present invention.

Pulse generator In Fig. 3 of the drawings there is illustrated a pulse generator which may be employed as a source of pulses. The generator shown in Fig. 3 comprises a suitable oscillator 1 and two output circuits 2 and 3 coupled to the load side of oscillator 1. Oscillator 1 is illustrated as being of the crystal controlled type, although the degree of stability inherent in this type of oscillator may not be necessary, and in such cases other forms of oscillators may be substituted. The arrangement and operation of oscillators of this nature is so well known that further description is not included in this specification. The circuit elements are preferably so chosen that the oscillator operates at a rate of one hundred kilocycles per second or thereabout.

The output circuits 2 and 3 are coupled to the output or plate circuit of the oscillator 1. For example, the plate or anode circuit of oscillator 1 may include a suitable coil or winding 4 and the inputs to output circuits 2 and 3 may include coils 5 and 6, respectively, shunted by suitable variable capacitors 7 and 3, respectively, to permit tuning of the output circuits 2 and 3 with respect to each other. The windings 5 and 6 are preferably loosely coupled to the coil 4 and the tuning means permits phase shift between the circuits 2 and 3 for a purpose to be explained more fully hereinafter. Each of output circuits 2 and 3 is arranged to convert the sine wave output of oscillator 1 into relatively sharp pulses by including high-Q inductances 9 and 10 as the anode loads or' heavily biased electron discharge devices 11 and 12, respectively, in circuits 2 and 3, respectively. Shock excitation of circuits 2 and 3 tends to produce high-frequency transient trains which are cut off at the rst reversal by unilateral devices 13 and 14, respectively, which shunt inductances 9 and 10, respectively. Crystal diodes have een found to be suitable for this purpose.

Referring to Fig. l1 of the drawings, there is illustrated at A the output of the oscillator 1 and at B typical transient waves set up in the output circuits, this figure representing the output of circuit 3. By reason of the inclusion of crystal diode 14, die transient curve at Fig. llB is limited to only one loop as shown in solid lines, the suppressed portion of each of the transients being inclicated in Fig. 11B by the dotted extensions of the curves.

The unsuppressed negative pulses are then amplified and inverted in suitable amplifiers 1S and 16, respectively, and delivered at low impedance by cathode followers 17 and 18, respectively. Referring again to Fig. 1l, there are represented at C the relatively narrow spaced-apart pulses of positive sense which appear across cathode resistor 19. lf the phase shift between circuits 2 and 3 is 180 degrees, the similar relatively narrow spaced-apart pulses of positive sense which appear across cathode resistor 20 of cathode follower stage 18 are as represented at D of Fig. ll.

The output circuits 2 and 3 thus are utilized to produce two sets of relatively sharp pulses which may be displaced with respect to times of occurrence by means of tunable secondary circuits.

Gne set of the foregoing pulses is used, in the present embodiment of rny invention, to excite a sequential pulse generator having one stage for each line in the calling group, two stages of which are shown in Fig. 5. For example, the sequential pulse generator may be a suitable type of ring circuit of which the arrangement shown in Fig. 5 is one form.

The second set of output pulses are fed, in the illustrated form of my invention, to a commutating circuit having an output circuit for each of the calling lines, as ten for example, and also to provide auxiliary or dummy pulses for purposes hereinafter described, as for example to enable or maintain operation of each ndcr during the temporary or accidental absence of pulses, as during dialing by the calling party, and to perform timing functions.

Sequential pulse generator There is illustratd in Fig. 5 of the drawings a suitable sequential pulse generator for use in carrying out the principles of my invention. As described heretofore, one set of pulses from the pulse generator shown in Fig. 3 is employed to drive or excite the ring circuit constituting the sequential pulse generator in the present embodiment of my invention. lt is understood that there is actually employed one stage for each line in the calling group, the output of the last stage being connected to drive the first stage. For convenience, only two stages are shown in the drawing. Each stage comprises an Eccles-Jordan circuit including electron discharge devices, as of the pentode type, represented by the numerals 30, 31 and 34, 35, respectively for the two stages shown. The output of each stage is coupled to a cathode follower including a suitable discharge device, as for example triodes 32 and 32a, respectively, in order to provide output at low impedance. The resulting square wave output pulses may be called gate pulses and are used for commutating the channel pulses and for gating the distributor as more fully described hereinafter.

Referring to each stage of the sequential pulse generator, the components are so disposed that the upper tubes of each stage constitute the "off" section, the anode of which is coupled by a suitable coupling capacitor, as 36M, to the input side of. the associated cathode follower stage. lf it is assumed that the upper discharge device 3l) of the first stage is conducting, the upper devices of the other stages are non-conducting and remain nonconducting until something occurs to trigger the next upper discharge device 34. When a pulse appears over conductor 33 from the pulse generator, it is amplified by a suitable amplifier 36 and then applied to the cathodes and suppressor electrodes of each upper device. The appearance of a positive pulse on the cathode of device 30 cuts olf the discharge device 3l). The higher anode potential thereby resulting is impressed upon the control electrode of the lower discharge device 31 in the tirst stage causing it to become conductive. At the same time, 

